Back to my 30W LED project, I have a small northbridge heatsink with a fan on it that I've mounted to the back of my LED.

I'd like to poer it from the LED driver, but it's constant current and pumps out 1A, whereas the fan is only 50mA.

Would there be a way to restrict the current to 50mA for the fan without a drop in voltage? it doesn't move a lot of air so I don't want to slow it down, but it seems to move enough to keep the LED cool.

just tested it, and looks like it works fine with the fan connected in parallel to the driver. But my meter may have been acting up when I took measurements because now I'm reading 14.6V @ 1.06A with or without the fan in parallel.

If you have a voltage source that might go as high as 52 V, and a load that wants to see no more than 12V, then the answer is a voltage regulator for the fan. Voltae regulator and fan are in series, and that string is in parallel with the LED.

If you don't need full speed out of the fan, it can be a 317HV and the fan will see 10 or 11 V in normal operation (normal being 12V across the LED). If you need full speed then go with an LDO regulator. Either way the regulator should be able to handle at least 60 V in to run reliably in a 52 V world.

OR, since you don't need tight regulation and we're talking only 50 mA, this can be as simple as a 20K resistor, 12V zener, and TIP29B or C pass transistor. Worst case transistor power dissipation is 2W, but the load is after all a fan so heat sinking should be minimal.